1. Field of the Invention
The present invention relates to an improved muffler having a function of arresting sparks which are apt to develop in exhaust systems of various internal combustion engines as well as in generators and often constitute a cause of fires.
2. Description of the Prior Art
An exhaust system of an internal combustion engine or a generator ordinarily used today tends to produce undesired sparks which lead to fires. So-called spark arresters or mufflers with a spark arresting function, therefore, need be used for fire protection particularly with motorcycles operated in the field, general-purpose engines and engine generators which are movable to any desired site for operation, lown mowers, tank trucks for transporting combustibles, dust collectors associated with buffing machines, etc. In many countries, furnishing such an instrument with a spark arrester or a muffler with a similar function to a spark arrester is a legal obligation and a minimum standard which such a spark arrester or muffler should clear for prevention of fires is established; the use of spark arresters which are short of the standard is inhibited.
In light of the above situation, various types of spark arresters and mufflers have heretofore been proposed. For example, U.S. Pat. No. 3,407,575 (Krizman) discloses a spark arrester which is constructed to whirl entering gases so that an outer shell of a double tube having a closed end may trap sparks, or carbon particles. Although the disclosed spark arrester may effectively arrest exhaust sparks, it creates another problem that turbulence tends to develop in the flow of the gases constituting a source of noise and, therefore, a muffler has to be backed up by the spark arrester.
Another known spark arrester is furnished with a netting in the form of a sack which is fixed to the outlet of a muffler or either one of opposite ends of an inlet pipe. Such an implementation, however, requires periodic cleaning because the netting tends to be stopped up to increase the back pressure and, thereby, deteriorate the engine performance.